Method, system and computer program product for organizing data

ABSTRACT

Methods, systems and computer program products for organizing semi-structured data into taxonomies are described. The semi-structured data is clustered into a plurality of clusters based on a plurality of attributes and the clusters are ranked relative to each other. The attributes are also ranked relative to each other based on a common ranking measure suitable for each of the attributes. The taxonomy may be represented as a hierarchical tree structure comprising a root node and a plurality of child nodes with the root node containing the semi-structured data and each of the child nodes containing data points of a cluster generated from the semi-structured data.

FIELD OF THE INVENTION

The present invention relates to the organization and/or summary of data and more particularly to the automatic organization of semi-structured data into concept hierarchies or taxonomies.

BACKGROUND

Electronic data resides in numerous different forms and formats. Data can be well structured, such as when stored in the form of tables in relational databases, or unstructured, such as when stored as plain text or emails. Much data is generally irregular and loosely defined and does not adhere to a strict schema or conform to a preset format. Semi-structured data contains both structured and unstructured components. Some examples of semi-structured data include:

-   Product catalogs: Catalogs typically have structured data fields     such as price, make and feature specifications but also have some     unstructured data such as a product description in the form of text. -   Call-center records: Such records typically contain details of the     customer, the call-taker, and descriptive text summarizing the call. -   Content managers: Documents in a repository typically include     meta-data such as the date of creation, the author, the originating     department, etc., in addition to the actual content of the document     which comprises unstructured data. -   Publication databases: Databases such as PUBMED and DBLP contain     various details of articles such as a date of publication, the names     of the author/s and the journal/conference name in addition to a     title and an abstract which comprise unstructured data.

A need exists to provide improved methods and systems for handling semi-structured data for a variety of reasons. One such reason is the explosive growth of information available on the World Wide Web (WWW), which is a high volume data source that cannot be constrained by a rigid schema. Another reason is the need for exchanging data between disparate systems and databases, which demands an extremely flexible format for representing the data. Yet another reason is the integration of several heterogeneous data sources, notwithstanding the individual data sources being highly structured.

Drivers of the growth of semi-structured data include:

-   The use of XML as a standard for information exchange over the     Internet. -   Advances in Natural Language Processing (NLP) and annotator tools     have resulted in conversion of a substantial amount of unstructured     data to semi-structured data. -   Semantic web and annotations.

As the volume of semi-structured data is growing exponentially, it is becoming increasingly necessary to organize this date in a comprehensible and navigable manner. Exponential growth of text data and unstructured data posed similar problems.

Web directories such as Yahoo, Google and Dmoz have shown that a hierarchical arrangement of documents is very useful for browsing a document collection. The Dmoz directory was manually created by about 52 thousand editors. Manually generated directories, more comprehensible and accurate than automatically generated directories, are not always feasible and require much effort and time for maintenance in a dynamic world. Therefore, Automatic Taxonomy Generation (ATG) methods are useful for automatically arranging documents into hierarchies.

Summarizing of web search results is an important application of ATG. Internet searches typically return thousands of results and ranked lists returned by search engines do not handle users' browsing needs efficiently. Most users respond by viewing only a few results and may thus miss much relevant information. Moreover the criterion used to rank the search results may not reflect a user's need. Organizing the search results in concept hierarchies summarizes the results and helps users in browsing those search results. However, predefined hierarchies and categories may not be useful in organizing query results, whether the hierarchies are generated automatically or manually. Post-retrieval document clustering provides superior results when query results are clustered to generate concept hierarchies.

Clustering of documents is thus an important part of ATG. The nodes at each level of a hierarchy of documents can be viewed as a clustering of the documents. Monothetic clustering algorithms assign documents to a cluster based on a single feature, whereas polythetic clustering algorithms assign documents to clusters based on multiple features. Known document clustering algorithms include the so-called K-means algorithm and its variants, hierarchical agglomerative clustering (HAC) methods and, more recently, graph partitioning methods. For K-means algorithms, the best performing similarity measure between documents is the cosine measure between two document vectors. HAC algorithms start with singleton documents as clusters, and iteratively merge the two most similar clusters. They differ in their choice of similarity measure between clusters. Once clustered the next important step is to assign proper labels to the clusters to render them comprehensible.

Polythetic ATG algorithms such as K-Means and HAC and monothetic ATG algorithms such as CAARD, DSP and Discover have been applied to unstructured data to automatically generate taxonomies. The Vivisimo Content Integrator <www.vivisimo.com> provides federated search or meta-search capabilities to public and private organizations. A federated search capability enables users to perform multiple searches at the same time through as many diverse informational sources as needed, whether the sources comprise internal documents, intranets, partner extranets, web sources, subscription services and databases, syndicated news feeds, or intelligence portals such as Hoover's. Vivisimo also provides a product called Clustering Engine which automatically clusters or organizes search results into categories that are intelligently selected from the words and phrases contained in the results or documents themselves.

Some of the more commonly used techniques for analysis and summary of structured data are multidimensional navigation and OLAP. Endeca search and guided navigation technology <www.endeca.com> enables multidimensional navigation of search results, identifies important dimensions or attributes for a current set of results and groups the results into relevant categories along each dimension. However Endeca does not rank the various dimensions or attributes nor cluster text or unstructured attributes.

Storage, indexing and searching of semi-structured data poses new challenges. U.S. Pat. No. 6,804,677, entitled “Encoding semi-structured data for efficient search and browsing”, issued to Shadman et al. on Oct. 12, 2004 and is assigned to Ori Software Development Ltd. The patent relates to a method for encoding XML tree data that includes the step of encoding semi-structured data into strings of arbitrary length in a way that maintains non-structural and structural information about the XML data, and enables indexing the encoded XML data in a way facilitates efficient search and browsing.

Searching a large volume of semi-structured data such as the Internet returns a large set of data that is not simply browsed and navigated. Automatic organization of search results into concept hierarchies assists in browsing and navigating the search results. Such taxonomies advantageously also summarize the search results. U.S. Pat. No. 6,606,620, entitled “Method and system for classifying semi-structured documents”, issued to Sundaresan et al. on Aug. 12, 2003 and is assigned to International Business Machines Corporation. The method and system disclosed in the patent requires predefined classes and training data for learning, which may be expensive and may not be exhaustive. Furthermore, as data in a repository is evolving, a need may arise to form new classes, which is not feasible if done manually.

Recent advancements in technology have made the storage, retrieval, search and handling of semi-structured data more feasible. However, predefined taxonomies are not of any real assistance for semi-structured data. Hence, for semi-structured data, a need exists for methods and systems that automatically discover or generate taxonomies.

SUMMARY

Embodiments of the present invention relate to methods, systems and computer program products for organizing semi-structured data in the form of automatically generated taxonomies. Important concepts in the data (attributes) are highlighted at each level of the hierarchy of the taxonomy. Embodiments of the present invention also provide means for summarizing data comprising a mixture of structured, unstructured and semi-structured data. The data may have different types of attributes, where each attribute type may be handled in a different manner.

According to an aspect of the present invention, there is provided a method for organizing semi-structured data into taxonomies. The method comprises the steps of clustering the semi-structured data into a plurality of clusters based on a plurality of attributes, ranking the plurality of clusters relative to each other, and ranking the attributes based on a common ranking measure suitable for ranking each of the attributes relative to each other. The attributes may be ranked based on entropy of data for each attribute.

According to another aspect of the present invention, there is provided a method for organizing semi-structured data into taxonomies. The method comprises the steps of generating a vocabulary of items from the semi-structured data based on a plurality of different attribute types and clustering the semi-structured data by applying monothetic clustering to items in the vocabulary and data samples of the semi-structured data that comprise the vocabulary items.

The vocabulary of items may be generated by:

for each categorical attribute, adding (attribute, value) pairs corresponding to all possible values of the categorical attribute to the vocabulary;

for each numerical attribute, clustering the data based on the numerical attribute, considering the numerical-attribute-based clusters as categorical attributes and adding corresponding (attribute, value) pairs to the vocabulary;

for each textual attribute, extracting all possible words or phrases occurring in the values of the attribute and adding corresponding (attribute, word/phrase) pairs to the vocabulary; and

for each annotated textual attribute, adding all possible (attribute, tag, tagged text) triplets to the vocabulary.

Clustering, in any of the aspects of the present invention, may be performed using a plurality of monothetic clustering algorithms that are selected based on the attribute types. The clusters may be ranked based on coverage provided by the number of data points in a cluster, distinctiveness of a cluster from other clusters, and/or average intra-cluster distance.

The taxonomies may be represented as hierarchical tree structures comprising a root node and a plurality of child nodes with the root node containing the semi-structured data and each of the child nodes containing data points of a cluster generated from the semi-structured data.

BRIEF DESCRIPTION OF THE DRAWINGS

A small number of embodiments are described hereinafter, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a flowchart of a method for organizing semi-structured data into a taxonomy based on tag-separated (TS) clustering;

FIG. 2 is a flowchart of a method for organizing semi-structured data into a taxonomy based on tag-mixed (TM) clustering; and

FIG. 3 is a schematic block diagram of a computer system with which embodiments of the present invention may be practised.

DETAILED DESCRIPTION

Embodiments of methods, systems and computer program products are described hereinafter for organizing semi-structured data into taxonomies. Use of the phrase ‘semi-structured data’ in this document is intended to mean data containing one of more of the following types of attributes: categorical, numerical, annotated text and text or unstructured.

Monothetic clustering algorithms identify a set of key concepts present in each of a collection of documents. For example, such concepts may comprise words that appear in the documents or phrases extracted from the documents by some form of natural language processing. Monothetic clustering of documents involves selecting subsets of such concepts, making the subsets the labels of clusters, and assigning documents containing a concept to the cluster having the concept as its label. Monothetic clustering algorithms can be used to generate taxonomies. To start with, a “Root” node is created containing all of a given set of documents. The clusters obtained by clustering the documents form the child nodes of the “Root” node. The process is recursively applied to each child node until a termination condition is reached to generate a hierarchy of nodes in which nodes at lower levels represent a more specific concept than nodes at a relatively higher level. For additional information in relation to monothetic clustering algorithms, the reader is referred to the text “Algorithms for Clustering Data”, by Jain A. K. and Dubes R. C., Prentice Hall, Englewood Cliffs, N.J., 1989.

Two methods for clustering semi-structured data to generate taxonomies that use monothetic algorithms are described hereinafter. The first is referred to as Tag-Separated (TS) clustering and the second is referred to as Tag-Mixed (TM) clustering.

Tag-Separated (TS) Clustering

A method for organizing semi-structured data into a taxonomy is based on tag-separated (TS) clustering. This method comprises the three main steps of clustering the data using attributes, ranking the clusters, and ranking the attributes. The attributes are ordered based on their rank. Within each attribute, single level labeled clusters are generated using a suitable monothetic algorithm selected based on the type of the particular attribute. The clusters are themselves ranked. The process is repeated recursively for each cluster to generate a concept hierarchy.

FIG. 1 is a flowchart of a method for organizing, semi-structured data into a taxonomy based on tag-separated (TS) clustering.

At step 110, data comprising or consisting of semi-structured data is input.

At step 120, an attribute is selected. The attribute's type is identified at step 130. Typical examples of attribute types include categorical attributes, numerical attributes, text or unstructured attributes, and attributes with annotated text.

At step 140, the data is clustered based on the attribute selected in step 120. The actual clustering algorithm used depends on the type of the attribute selected:

-   For categorical attributes, each category constitutes a single     cluster. The number of clusters is thus the same as the number of     categories. The categories are ranked based on the coverage, that     is, the number of data points having the attribute value equal to a     category. -   For numerical attributes, traditional clustering algorithms such as     K-Means and HAC can be used to cluster the data projected onto the     range of the numerical attribute. However, other algorithms such as     algorithms based on valley detection and model selection and mode     hunting algorithms in an EM framework may also be used. -   Various monothetic document clustering algorithms such as CAARD,     Discover and DSP can be used to cluster data with respect to text     attributes. The CAARD clustering algorithm is briefly described     hereinafter and the reader is referred to a paper by Krishna K. and     Krishnapuram R., entitled “A Clustering Algorithm for Asymmetrically     Related Data with its Applications to Text Mining”, CIKM-2001,     Atlanta, USA, November 2001, pp. 571-573, for additional     information. For additional information in relation to the DSP     clustering algorithm, the reader is referred to a paper by     Lawrie D. J. and Croft W. B., entitled “Generating hierarchical     summaries for web searches”, in Proceedings of SIGIR, 2003, pp.     457-458. For additional information in relation to the Discover     clustering algorithm, the reader is referred to a paper by Kummamuru     K., Lotlikar R., Roy S., Singal K. and Krishnapuram R., entitled “A     Hierarchical Monothetic Document Clustering Algorithm for     Summarization and Browsing Search Results”, in Proceedings of WWW,     New York, USA, May 17-22, 2004. Each of the three foregoing papers     relating to monothetic clustering algorithms is incorporated herein     in their entirety by reference. -   Annotated text attributes can be clustered using non-mixed tag     clustering or mixed tag clustering.     -   In non-mixed tag clustering, a separate vocabulary is         constructed using the text appearing with each tag. That is,         there is a vocabulary corresponding to each tag appearing in the         annotated text. Any monothetic clustering algorithm can         generally be used to find clusters within each vocabulary. Once         clusters are found, a data point is assigned to a cluster if the         data point has the cluster label within the corresponding tag.         This approach yields a hierarchy of clusters with two levels.         The first level comprises various annotations/tags and the         second level comprises clusters derived from corresponding         tag-specific vocabulary. The clusters in the first level are         ranked based on entropy of the distribution of data across         clusters in the second level, which is explained hereinafter.     -   In mixed tag clustering, a single vocabulary comprising tokens         representing (tag, value) pairs is generated. Any monothetic         clustering algorithm can generally be applied to generate the         clusters using this single vocabulary.

At step 150, the clusters obtained with respect to each attribute are ranked for ordering. Various ranking criteria can be used and the ranking will depend on the type of attribute to which the clusters belong. Some examples of ranking criteria include coverage (the number of data points in the cluster), coverage along with distinctiveness and average intra-cluster distance. For additional information in relation to distinctiveness, the reader is referred to a paper by Kummamuru K., Lotlikar R., Roy S., Singal K. and Krishnapuram R., entitled “A Hierarchical Monothetic Document Clustering Algorithm for Summarization and Browsing Search Results”, in Proceedings of WWW, New York, USA, May 17-22, 2004, as incorporated by reference hereinbefore. For the purpose of browsing search results, coverage is the most important criterion.

At step 160, a determination is made whether more attributes are to be processed. If so (YES), processing returns to step 120 for selection of the next attribute. If not (NO), processing continues at step 170.

At step 170, the attributes are ranked based on a common measure that is suitable for each of the different attributes. In one embodiment, entropy along an attribute is used as a measure to rank the attributes by:

-   Generating a cluster for each attribute using the method described     in step 140. -   Calculating the entropy of each attribute based on the cluster     generated along that attribute (described hereinafter) and ranking     the attributes to generate a summary.

The number of clusters used to calculate the entropy may be limited to the top few clusters. For example, the top few clusters may comprise the top few clusters in the ranked list of clusters (as per step 150). Alternatively top clusters may be selected to cover a pre-determined percentage of the data (e.g., the top ranked n clusters may be selected, where n takes a value such that 90% of the data is covered).

Computation of Attribute Entropy Based on Generated Clusters

Let n_(ij) denote the number of data points in the jth cluster of ith attribute.

Let N_(i) denote the number of clusters with respect to ith attribute.

Let $p_{ij} = {n_{ij}/{\sum\limits_{l = 1}^{N_{i}}n_{il}}}$ where p_(ij) is the probability that a data point belongs to jth cluster while clustering along the ith attribute.

Then, the entropy E_(i) of the ith attribute is given by: $E_{i} = {\sum\limits_{j = 1}^{N_{i}}{p_{ij}\log\quad\left( p_{ij} \right)}}$

As the attributes are of different types and different clustering algorithms may be used to cluster the data along the attributes, the entropy computed for an attribute will be dependent on the algorithm used and its parameters.

In an alternative embodiment also using entropy as a ranking measure, the entropy of the data along each attribute is calculated and the attributes are ranked based on this entropy. Then for each attribute in the ranked list, data is clustered along the attribute. This will shield against bias generated due to variations in clustering algorithm for different attributes and/or variations in parameters of the clustering algorithm.

Although the embodiments described employ entropy as a ranking criterion, any other ranking criterion which is suitable across different types of attributes can be used. Examples of other ranking criteria that may be used include cluster cohesiveness and the Pseudo F statistic. For additional information in relation to cluster cohesiveness, the reader is referred to the text “Algorithms for Clustering Data”, Jain A. K. and Dubes R. C., Prentice Hall, Englewood Cliffs, N.J., 1989. For additional information in relation to the Pseudo F statistic, the reader is referred to “A dendrite method for cluster analysis”, Calinski T. and Harabasz J., Communications in Statistics, 3:1-27, 1974.

Tag-Mixed (TM) Clustering

Another method for organizing semi-structured data into taxonomy is based on tag-mixed (TM) clustering. This involves construction of a vocabulary of (attribute value) pairs and/or tuples based on the data. Numerical attributes are clustered and converted to categorical attributes before being added to the vocabulary. A categorical attribute with n possible categorical values results in n (attribute, value) pairs in the vocabulary. Textual attributes result in (attribute, word/phrase) pairs in the vocabulary, where the word/phrase appears as the value of the attribute. Annotated text attributes result in (attribute, tag, value) tuples in the vocabulary, where ‘value’ represents a word or phrase appearing in the tagged text. Thus the constructed vocabulary consists of (attribute, value) pairs and/or (attribute, tag, value) tuples, which are also referred to as tokens. Once the vocabulary has been constructed, a monothetic clustering algorithm (e.g., as referred to hereinbefore) can be used to generate a taxonomy of the data.

FIG. 2 is a flowchart of a method for organizing semi-structured data into a taxonomy based on tag-mixed (TM) clustering.

At step 210, data comprising or consisting of semi-structured data is input.

Step 220 comprises sub-steps 221 to 226 for constructing a vocabulary based on the data input in step 210. The different attribute types are considered or processed in substantially the same way except for numerical attributes. Numerical attributes are first clustered and each cluster is considered as a category. Numerical attributes are thus converted to categorical attributes.

At step 221, an attribute is selected. At step 222, a determination is made whether the selected attribute is numerical. If so (YES), the attribute is clustered at step 223. Then, at step 224, each cluster is treated as a category and the numerical attribute is converted to a categorical attribute. All possible values of the attribute are added to the vocabulary at step 225. If the selected attribute is non-numerical (NO), at step 222, processing proceeds directly to step 225 where all possible values of the attribute are added to the vocabulary.

After step 225, a determination is made at step 226 whether more attributes are to be processed. If so (YES), processing continues at step 222, where the next attribute is selected. If not (NO), processing continues at step 230.

The constructed vocabulary consists of (attribute, value) pairs and/or (attribute, tag, value) tuples, also known as tokens.

Each data sample is represented as a set of tokens where each token is contained in the data sample and is part of the vocabulary. An inverted index for a given data set and a vocabulary contains each token in the vocabulary with reference to all the data samples containing that token.

An inverted index for the vocabulary is initialized at step 230 and a representation of each data sample is created at step 240, which comprises sub-steps 241 to 245. A data sample is selected at step 241. At step 242, a determination is made as to the attribute type of the data sample selected at step 241. If the attribute type is categorical or numerical (step 243), there exists a single token or (attribute, value) pair. Alternatively, if the attribute type is text (step 244), multiple tokens or (attribute, phrase) pairs exist for each text phrase. Alternatively, if the attribute type is annotated text (step 245), multiple tokens or (attribute, tag, text) tuples exist. After each of steps 243, 244 and 245, the relevant representation of the data sample selected in step 241 is added to the inverted index at step 246.

At step 247, a determination is made whether any more data samples need to be processed. If so (Y), processing returns to step 241 for selection of the next data sample. If not (N), monothetic clustering is applied to the data samples using the data in the inverted index at step 250.

The CAARD Monothetic Clustering Algorithm

The CAARD monothetic clustering algorithm is briefly described hereinafter with reference to the tag-mixed method of FIG. 2:

-   1. Once the vocabulary has been determined (step 220 of FIG. 2), an     inverse index is created containing a list of data samples that     contain a given vocabulary item.

Let e_(l), . . . , e_(n) be the n entries in the vocabulary. Then, let l_(l), . . . , l_(n) be the n corresponding sets of numbers that indicate the list of data items containing the corresponding vocabulary entry. That is, each l_(i) indicates a list of all data items containing e_(i).

-   2. The clustering algorithm computes inclusion of one entry into     another. Inclusion of e_(i) into e_(j) is given by the formula     l_(i)∩l_(j)/|l_(j)|, where |l_(j)| represents the number of elements     in l_(j). -   3. The set of data clusters are represented by their representatives     which are entries in the vocabulary. -   4. A set of the representatives S is generated by considering the     vocabulary entries in descending order of their frequency. -   5. The first entry in the order is added to S. Then, each     consecutive entry is added to one of the existing clusters C_(i); if     the entry is included into the corresponding representative r_(i) in     S by more than a defined threshold. If the data sample is not     related to any of the existing entries in S by more than the     threshold, the data sample is added to S. That is, a new cluster is     formed with this entry as its representative. -   6. Once the set of representatives S is generated, each data sample     is assigned to a cluster if the cluster's representative is     contained in the data sample. Hence, each data sample could belong     to more than one cluster. If a data sample does not belong to any of     the clusters, then the data sample is assigned to a ‘miscellaneous’     cluster.

A more detailed description of the CAARD clustering algorithm is available in a paper by Krishna K. and Krishnapuram R., entitled “A Clustering Algorithm for Asymmetrically Related Data with its Applications to Text Mining”, CIKM-2001, Atlanta, USA, November 2001, pp. 571-573, which is incorporated herein in its entirety by reference.

However, it should be noted that other monothetic clustering algorithms such as DSP and Discover can be used in place of the CAARD algorithm. For additional information in relation to the DSP clustering algorithm, the reader is referred to a paper by Lawrie D. J. and Croft W. B., entitled “Generating hierarchical summaries for web searches”, in Proceedings of SIGIR, 2003, pp. 457-458. For additional information in relation to the Discover clustering algorithm, the reader is referred to a paper by Kummamuru K., Lotlikar R., Roy S., Singal K. and Krishnapuram R., entitled “A Hierarchical Monothetic Document Clustering Algorithm for Summarization and Browsing Search Results”, in Proceedings of WWW, New York, USA, May 17-22, 2004. Both of the foregoing papers relating to monothetic clustering algorithms are incorporated herein in their entirety by reference.

EXAMPLE TAXONMIES

Examples of taxonomies generated on a set of bibliographic entries are shown hereinafter.

Table 1 shows a sample of bibliographic entries in the DBLP database, which provides bibliographic information on major computer science journals and proceedings. TABLE 1 <inproceedings mdate=“2002-12-17” key=“conf/kdd/AgrawalP95”> <author>Rakesh Agrawal</author> <author>Giuseppe Psaila</author> <title>Active Data Mining.</title> <pages>3-8</pages> <year>1995</year> <booktitle>KDD</booktitle> <url>db/conf/kdd/kdd95.html#AgrawalP95</url> </inproceedings> <inproceedings mdate=“2002-12-17” key=“conf/kdd/AgrawalS96”> <author>Rakesh Agrawal</author> <author>Kyuseok Shim</author> <title>Developing Tightly-Coupled Data Mining Applications on a Relational Database System.</title> <pages>287-290</pages> <year>1996</year> <booktitle>KDD</booktitle> <url>db/conf/kdd/kdd96.html#AgrawalS96</url> </inproceedings> <inproceedings mdate=“2004-03-31” key=“conf/icde/AgrawalCDN03”> <author>Rakesh Agrawal</author> <author>Surajit Chaudhuri</author> <author>Abhinandan Das</author> <author>Vivek R. Narasayya</author> <title>Automating Layout of Relational Databases.</title> <pages>607-618</pages> <year>2003</year> <crossref>conf/icde/2003</crossref> <booktitle>ICDE</booktitle> <url>db/conf/icde/icde2003.html#AgrawalCDN03</url> </inproceedings> <inproceedings mdate=“2004-03-31” key=“conf/icde/Agrawal03”> <author>Rakesh Agrawal</author> <title>Database Technologies for E-Commerce.</title> <pages>801</pages> <ee>http://csdl.computer.org/comp/proceedings/icde/2003/2071/00/20710801abs.htm</ee> <year>2003</year><crossref>conf/icde/2003</crossref> <booktitle>ICDE</booktitIe> <url>db/conf/icde/icde2003.html#Agrawal03</url> </inproceedings>

Table 2 shows a portion of a taxonomy generated using the Tag-Separated (TS) method described hereinbefore with reference to FIG. 1 from a subset of the DBLP database, a sample extract of which is shown in Table 1. As may be seen from Table 2, the nodes at the first level represent the attributes such as ‘AUTHOR’ and ‘BOOKTITLE’ and the nodes at the second level represent the values of that attributes. For example nodes within the attribute node ‘AUTHOR’ represent the authors ‘Ramakrishnan Srikant’ and ‘H. V. Jagdish’. TABLE 2 <ROOT LABEL= “Rakesh Agrawal”> <NODE LABEL = AUTHOR> <NODE LABEL = “Ramakrishnan Srikant” > <pub> <article mdate = 2003-11-20 key = journals/tkde/AgrawalS03 > <author>Rakesh Agrawal</author> <author>Ramakrishnan Srikant</author> <title>Searching with Numbers.</title> <pages>855-870</pages> <year>2003</year> <volume>15</volume> <journal>IEEE Trans. Knowl. Data Eng.</journal> <number>4</number> <ee>http://csdl.computer.org/comp/trans/tk/2003/04/k0855abs.htm</ee> <url>db/journals/tkde/tkde15.html AgrawalS03</url> </article> </pub> </NODE> <NODE LABEL = “H. V. Jagadish”> <pub> <article mdate = 2003-11-28 key = journals/debu/AgrawalJ89 > <author>Rakesh Agrawal</author><author>H. V. Jagadish</author> <title>Multiprocessor Transitive Closure Algorithms.</title> <pages>30-36</pages> <year>1989</year> <volume>12</volume> <journal>IEEE Data Eng. Bull.</journal> <number>1</number> <url>db/journals/debu/debu12.html AgrawalJ89</url> </article> </pub> </NODE> </NODE> <NODE LABEL = BOOKTITLE> <NODE LABEL = “VLDB”> <pub> <inproceedings mdate = 2002-01-03 key = conf/vldb/AgrawalJ87 > <crossref>conf/vldb/87</crossref> <author>Rakesh Agrawal</author> <author>H. V. Jagadish</author> <title>Direct Algorithms for Computing the Transitive Closure of Database Relations.</title> <pages>255-266</pages> <year>1987</year> <booktitle>VLDB</booktitle> <url>db/conf/vldb/vldb87.html AgrawalJ87</url> <cite>...</cite> <cite>conf/vldb/DeWittG85</cite> <cite>...</cite> </inproceedings> </pub> </NODE> <NODE LABEL = “ICDE”> <pub> <inproceedings mdate = 2003-11-14 key = conf/icde/Agrawal03 > <author>Rakesh Agrawal</author> <title>Database Technologies for E-Commerce.</title> <pages>801</pages> <year>2003</year> <crossref>conf/icde/2003</crossref> <booktitle>ICDE</booktitle> <url>db/conf/icde/icde2003.html Agrawal03</url> </inproceedings> </pub> </NODE> </NODE:BOOKTITLE> </ROOT>

Table 3 shows a portion of a taxonomy generated using the Tag-Mixed (TM) method described hereinbefore with reference to FIG. 2. TABLE 3 <ROOT LABEL= “Rakesh Agrawal”> <NODE TAG = AUTHOR; VALUE = “Ramakrishnan Srikant” > <pub> <article mdate = 2003-11-20 key = journals/tkde/AgrawalS03 > <author>Rakesh Agrawal</author> <author>Ramakrishnan Srikant</author> <title>Searching with Numbers.</title> <pages>855-870</pages> <year>2003</year> <volume>15</volume> <journal>IEEE Trans. Knowl. Data Eng.</journal> <number>4</number> <ee>http://csdl.computer.org/comp/trans/tk/2003/04/k0855abs.htm</ee> <url>db/journals/tkde/tkde15.html AgrawalS03</url> </article> </pub> </NODE > <NODE TAG = BOOKTITLE; VALUE = “VLDB”> <pub> <inproceedings mdate = 2002-01-03 key = conf/vldb/AgrawalJ87 > <crossref>conf/vldb/87</crossref> <author>Rakesh Agrawal</author> <author>H. V. Jagadish</author> <title>Direct Algorithms for Computing the Transitive Closure of Database Relations.</title> <pages>255-266</pages> <year>1987</year> <booktitle>VLDB</booktitle> <url>db/conf/vldb/vldb87.html AgrawalJ87</url> <cite>...</cite> <cite>conf/vldb/DeWittG85</cite> <cite>...</cite> </inproceedings> </pub> </NODE> </ROOT>

The vocabulary of the database shown in Table 3 comprises the following entries:

The numerical attribute <year> is clustered. Assuming that the years are clustered into decades, the values of the year attributes are mapped to the appropriate decade. The corresponding vocabulary would contain entries such as (year, 2000-10), (year, 1990-2000), and (year, 1980-90).

The attributes such as <author> and <booktitle> are categorical, which take one of a pre-specified number of values. The corresponding vocabulary entries would be (author, “Rakesh Agrawal”), (author, “Surajit Chaudhuri”), (booktitle, ICDM), (booktitle, ICML).

The attributes such as <title> are textual and the vocabulary corresponding to the <title> attribute contains entries such as (title, Automating), (title, Relational) and (title, Databases). If the <title> tag is annotated with proper nouns then a corresponding vocabulary entry would be (title, proper-noun, “Relational Databases”).

The foregoing tables 2 and 3 constitute examples of bibliographic entries organized into taxonomies and are of an illustrative nature only. In particular, the methods described hereinbefore are applicable to any semi-structured data and are by no means limited to the type of data shown in the foregoing examples.

Computer Hardware and Software

FIG. 3 shows a schematic block diagram of a computer system 300 that can be used to practice the methods described herein. More specifically, the computer system 300 is provided for executing computer software that is programmed to assist in performing methods for organizing semi-structured data into taxonomies. The computer software executes under an operating system such as MS Windows 2000, MS Windows XP™ or Linux™ installed on the computer system 300.

The computer software involves a set of programmed logic instructions that may be executed by the computer system 300 for instructing the computer system 300 to perform predetermined functions specified by those instructions. The computer software may be expressed or recorded in any language, code or notation that comprises a set of instructions intended to cause a compatible information processing system to perform particular functions, either directly or after conversion to another language, code or notation.

The computer software program comprises statements in a computer language. The computer program may be processed using a compiler into a binary format suitable for execution by the operating system. The computer program is programmed in a manner that involves various software components, or code, that perform particular steps of the methods described hereinbefore.

The components of the computer system 300 comprise: a computer 320, input devices 310, 315 and a video dsiplay 390. The computer 320 comprises: a processing unit 340, a memory unit 350, an input/output (I/O) interface 360, a communications interface 365, a video interface 345, and a storage device 355. The computer 320 may comprise more than one of any of the foregoing units, interfaces, and devices.

The processing unit 340 may comprise one or more processors that execute the operating system and the computer software executing under the operating system. The memory unit 350 may comprise random access memory (RAM), read-only memory (ROM), flash memory and/or any other type of memory known in the art for use under direction of the processing unit 340.

The video interface 345 is connected to the video dsiplay 390 and provides video signals for display on the video dsiplay 390. User input to operate the computer 320 is provided via the input devices 310 and 315, comprising a keyboard and a mouse, respectively. The storage device 355 may comprise a disk drive or any other suitable non-volatile storage medium.

Each of the components of the computer 320 is connected to a bus 330 that comprises data, address, and control buses, to allow the components to communicate with each other via the bus 330.

The computer system 300 may be connected to one or more other similar computers via the communications interface 365 using a communication channel 385 to a network 380, represented as the Internet.

The computer software program may be provided as a computer program product, and recorded on a portable storage medium. In this case, the computer software program is accessible by the computer system 300 from the storage device 355. Alternatively, the computer software may be accessible directly from the network 380 by the computer 320. In either case, a user can interact with the computer system 300 using the keyboard 310 and mouse 315 to operate the programmed computer software executing on the computer 320.

The computer system 300 has been described for illustrative purposes. Accordingly, the foregoing description relates to an example of a particular type of computer system such as a personal computer (PC), which is suitable for practicing the methods and computer program products described hereinbefore. Those skilled in the computer programming arts would readily appreciate that alternative configurations or types of computer systems may be used to practice the methods and computer program products described hereinbefore.

Embodiments of methods, systems and computer program products have been described hereinbefore for organizing semi-structured data into taxonomies. The foregoing detailed description provides exemplary embodiments only, and is not intended to limit the scope, applicability or configurations of the invention. Rather, the description of the exemplary embodiments provides those skilled in the art with enabling descriptions for implementing an embodiment of the invention. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention as set forth in the claims hereinafter.

Where specific features, elements and steps referred to herein have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. Furthermore, features, elements and steps referred to in respect of particular embodiments may optionally form part of any of the other embodiments unless stated to the contrary. 

1. A method for organizing semi-structured data into a taxonomy, said method comprising: clustering said semi-structured data into a plurality of clusters based on a plurality of attribute types; ranking said plurality of clusters relative to each other; and ranking said attributes relative to each other based on a ranking measure.
 2. The method of claim 1, wherein said clustering is performed using a plurality of monothetic clustering algorithms, wherein said algorithms are selected based on said attribute types.
 3. The method of claim 1, wherein said plurality of attribute types comprise at least one of: numerical attributes; categorical attributes; text attributes; and annotated text attributes.
 4. The method of claim 1, wherein said clusters are ranked based on at least one criterion comprising at least one of: coverage provided by the number of data points in a cluster; distinctiveness of a cluster from other clusters; and average intra-cluster distance.
 5. The method of claim 1, wherein said attributes are ranked based on entropy of data for each attribute.
 6. The method of claim 1, further comprising representing said taxonomy as a hierarchical tree structure comprising a root node and a plurality of child nodes, said root node containing said semi-structured data and said each of said child nodes containing data points of a cluster generated from said semi-structured data.
 7. A method for organizing semi-structured data into a taxonomy, said method comprising: generating a vocabulary of items from said semi-structured data based on a plurality of different attribute types; and clustering said semi-structured data by applying monothetic clustering to items in said vocabulary and data samples of said semi-structured data that comprise said items.
 8. The method of claim 7, wherein said plurality of different attribute types comprise at least one of: numerical attributes; categorical attributes; text attributes; and annotated text attributes.
 9. The method of claim 8, wherein said generating a vocabulary comprises: for each numerical attribute of said plurality of attributes: clustering said semi-structured data based on said numerical attribute; and treating said numerical attribute based cluster as a categorical attribute; and adding all possible values of each of said plurality of attributes to said vocabulary.
 10. The method of claim 7, wherein said generating a vocabulary of items comprises: for each categorical attribute, adding attribute value pairs corresponding to all possible values of the categorical attribute to the vocabulary; for each numerical attribute, clustering the data based on the numerical attribute, considering the numerical-attribute-based clusters as categorical attributes and adding corresponding attribute value pairs to the vocabulary; for each textual attribute, extracting all possible words or phrases occurring in the values of the attribute and adding corresponding attribute word/phrase pairs to the vocabulary; and for each annotated textual attribute, adding all possible attribute tag tagged text triplets to the vocabulary.
 11. The method of claim 7, wherein said clustering is performed using a plurality of monothetic clustering algorithms, wherein said algorithms are selected based on said attribute types.
 12. The method of claim 7, further comprising representing said taxonomy as a hierarchical tree structure comprising a root node and a plurality of child nodes, said root node containing said semi-structured data and each of said child nodes containing data points of a cluster generated from said semi-structured data.
 13. An apparatus for organizing semi-structured data into a taxonomy, said apparatus comprising: a memory unit for storing data and instructions; and a processing unit coupled to said memory unit, said processing unit programmed to: perform said instructions; cluster said semi-structured data into a plurality of clusters based on a plurality of attribute types; rank said plurality of clusters relative to each other; and rank said attributes relative to each other based on a ranking measure.
 14. The apparatus of claim 13, wherein said processing unit is programmed to perform said clustering using a plurality of monothetic clustering algorithms, wherein said algorithms are selected based on said attribute types.
 15. An apparatus for organizing semi-structured data into a taxonomy, said apparatus comprising: a memory unit for storing data and instructions; and a processing unit coupled to said memory unit, said processing unit programmed to: perform said instructions; generate a vocabulary of items from said semi-structured data based on a plurality of different attribute types; and cluster said semi-structured data by applying monothetic clustering to items in said vocabulary and data samples of said semi-structured data that comprise said items.
 16. The apparatus of claim 15, wherein said processing unit is programmed to: for each categorical attribute, add attribute value pairs corresponding to all possible values of the categorical attribute to the vocabulary; for each numerical attribute, cluster the data based on the numerical attribute, treat the numerical-attribute-based clusters as categorical attributes and add corresponding attribute value pairs to the vocabulary; for each textual attribute, extract all possible words or phrases occurring in the values of the attribute and add corresponding attribute word/phrase pairs to the vocabulary; and for each annotated textual attribute, add all possible attribute tag tagged text triplets to the vocabulary.
 17. A computer program product comprising a computer readable medium comprising a computer program recorded therein for organizing semi-structured data into a taxonomy, said computer program product performing a method comprising: computer program code for clustering said semi-structured data into a plurality of clusters based on a plurality of attribute types; ranking said plurality of clusters relative to each other; and ranking said attributes relative to each other based on a ranking measure.
 18. The computer program product of claim 17, wherein said clustering comprises a plurality of monothetic clustering algorithms, wherein said algorithms are selected based on said attribute types.
 19. A computer program product comprising a computer readable medium comprising a computer program recorded therein for organizing semi-structured data into a taxonomy, said computer program product perform ing a method comprising: generating a vocabulary of items from said semi-structured data based on a plurality of different attribute types; and clustering said semi-structured data by applying monothetic clustering to items in said vocabulary and data samples of said semi-structured data that comprise said items.
 20. The computer program product of claim 19, wherein said method further comprises: computer program code for adding attribute value pairs corresponding to all possible values of each categorical attribute to the vocabulary; computer program code for clustering the data based on each numerical attribute, treating the numerical-attribute-based clusters as categorical attributes and adding corresponding attribute value pairs to the vocabulary; computer program code for extracting all possible words or phrases occurring in the values of each textual attribute and adding corresponding attribute word/phrase pairs to the vocabulary; and computer program code for adding all possible attribute tag tagged text triplets for each annotated textual attribute to the vocabulary. 